mac80211: make simple rate control algorithm built-in

Too frequently people do not have module autoloading enabled
or fail to install the rate control module correctly, hence
their hardware probing fails due to no rate control algorithm
being available. This makes the 'simple' algorithm built into
the mac80211 module unless EMBEDDED is enabled in which case
it can be disabled (eg. if the wanted driver requires another
rate control algorithm.)

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>